Github user paul-rogers commented on the issue:
https://github.com/apache/drill/pull/1014
Not sure the description here is entirely correct. Let's separate two
concepts: the plugin (code) and the plugin definition (the stuff in JSON.)
Plugin definitions are stored in ZK and retrieved by the Foreman. There may
be some form of race condition in the Foreman, but that's not my focus here.
The plugin *definition* is read by the Forman and serialized into the
physical plan. Each worker reads the definition from the physical plan. For
this reason, the worker's definition can never be out of date: it is the
definition used when serializing the plan.
Further, Drill allows table functions which provide query-time name/value
pair settings for format plugin properties. The only way these can work is to
be serialized along with the query. So, the actual serialized format plugin
definition, included with the query, includes both the ZK information and the
table function information.
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